1. Field of the Invention
The present invention relates to a thrust ball bearing used in a driving mechanism such as a scroll compressor and the like. More particularly, the present invention relates to a rotation preventing mechanism composed of a thrust ball bearing for improving the assembly characteristics thereof when it is mounted on a structural member, and to a scroll type compressor using the rotation preventing mechanism.
2. Description of the Related Art
Conventionally, scroll type compressors are used in refrigerant circuits for air conditioning apparatuses for vehicles and the like. The scroll type compressor includes a stationary swirl or scroll member fixed in a casing and a movable swirl or scroll member disposed in the casing similarly in confrontation with the stationary scroll member. The movable swirl member executes a turning motion while the rotation thereof is prevented by a rotation preventing mechanism with respect to the stationary swirl member, compresses refrigerant drawn into the casing and discharges the compressed refrigerant to a refrigerant circuit disposed outside the scroll type compressor.
A rotation preventing mechanism is used for preventing the rotation in itself or the revolution around a center line of the stationary swir member and composed of a thrust ball bearing. The thrust ball bearing includes a first race fixed in a casing, a first ring, a second race disposed to the back surface of a movable scroll member, a second ring, and thrust balls interposed between the first and second rings.
The first ring and the first race are arranged integrally with each other to thereby form a first race section, whereas the second ring and the second race are arranged integrally with each other to thereby form a second race section.
In the conventional thrust ball bearing, thrust balls are accommodated in annular ball accommodating grooves which are formed at the confronting surfaces of the first and second race sections, respectively.
In each of the ball accommodating grooves of the race sections of the conventional thrust ball bearing, however, since the groove is in contact with a thrust ball through a convex portion inside a groove bottom portion and through a concave portion outside it, the contact area of the groove and the thrust ball is smaller inside the groove bottom portion. Accordingly, the inner portion of the ball accommodating groove is more stressed and wears more quickly, whereby the life of the thrust ball bearing is shortened.